This invention relates generally to electromagnetic devices having armatures that reciprocate between two stable, alternative positions, and it relates more particularly to a bi-stable electromagnetic device that is useful for actuating contacts of an electric current reverser.
While useful in a variety of electrical or mechanical applications, the invention will be herein disclosed in the context of a bi-stable or double-throw electric current reverser for the electrical propulsion system of a traction vehicle such as a rapid transit car. For this particular application, the electromagnetic device needs to be sufficiently rugged and reliable to withstand physical shock and vibration and temporary loss of control power without unlatching. That is, the contact-carrying armature of the bi-stable device must be held firmly in a preselected position and must not move to its other position when the mounting base of the device is subjected to physical forces of relatively high amplitude and/or when control power for the operating coils is interrupted.
One known approach to obtaining the required holddown or latching function in a bi-stable electromagnetic device is to utilize an overcenter toggle mechanism. However, such mechanisms are undesirably large and expensive, are complicated to adjust, and tend to be less reliable than required for many applications.
Another known approach is to utilize permanent magnets for releasably latching the armature of an electromagnetic device in either of two stable positions. Prior art U.S. Pat. Nos. 3,001,049; 3,621,419; and 4,286,244 are exemplary.